This invention relates to a needle-horn configuration which significantly reduces the heat generated in the needle. Available needles may become hot enough to damage the cornea tissue on the incision through which the needle penetrates into the anterior chamber of the eye.
To date there is a significant number of needles with different characteristics. A careful analysis of their similarities and differences would show that their effect on the needle performances is minimal. Some have smooth surfaces and some striated surfaces. Some have left handed threads and others have right handed threads. To minimize the size of the incision some needles have smaller diameters than others. The configurations of the tips themselves may also vary from needle to needle, but none of the available needles have tips which are hydrodynamically significantly better than the others. In other words, their suction power is roughly the same and relatively low.
All needles analyzed to date use the same type of attachment: horn with internal thread and needle with external thread. It is the main, and extremely important, technical advantage of our invention that we exchange the positions of the threads in the horn and in the needle. In one of the embodiments the needle has the internal thread while the horn has the external thread. With this arrangement the ultrasound waves may travel in an almost continuous and uniform path from the transducer to the tip of the needle. Furthermore, our design includes an element that it is not used by any other needle. Presently available needles establish direct contact between the horn's vertical front end surface and the mating vertical surface of the needle hub. Both the horn and the needle are made of titanium alloy (Ti-6Al-4V) in a relatively hard condition. It would be technically impossible that both surfaces were perfectly planar and parallel using the technology used at present. The areas of contact would be a small percent of the total area. The ultrasound waves would be reflected back by the contact free areas of the horn. Because of the needle hub geometries in use today, even those waves that cross the areas of contact would be subjected to multiple reflections within the hub with the consequent generation of significant amounts of heat and increasing temperatures in the hub and needle.
The problems described in the previous paragraph are eliminated in our invention. The interface problem is eliminated by placing a 0.005″ thick washer of annealed and magnetized pure nickel. Such a washer could be in a range of about 0.002″ to 0.050″ in thickness. The washer has the same internal diameter as both the horn and the needle. The outside diameter of the washer is equal to the outside diameter of the horn front surface. When the needle and the horn are tightened together the applied torque will generate enough pressure on the washer that it will deform completely filling the space between the end surfaces of the horn and the needle hub. Two positive effects will take place due to the tightening of the needle-horn joint. The gaps resulting from the machining irregularities will be eliminated and, because Ni has an ultrasound speed very close to that of Ti-6Al-4V, a large percentage of the arriving waves will go through the interface with minimum losses and great reduction in heat generation.